Perhaps this shouldn't be here but I wanted to take further a point Rob made about the Penthouses. When originally built they were two-room suite as shown on the plans below. There were ten of them with the two top suites being called Trafalgar and Queen Anne - these were originally over two decks. The two-room suites were named Pall Mall, Grosvenor, Kensington, Mayfair, Piccadilly, Westminster, Buckingham and Chelsea.
The suites were later all made one room = 20 Penthouses. However, for those willing to pay they could still be set up as two room units and you could have the choice of going either upstairs or downstairs to be in the Queen Anne and Queen Victoria Suites (the Trafalgar name was changed in 1999).